A mastery of water-use techniques by civilization has been evidenced for thousands of years, one high point being reached with the development by the Romans of long-distance water transportation. Within the current century, the introduction of practical turbine pumps, large scale water storage and practical water transmission networks has greatly expanded public water supply systems. See in this regard:
I. "Technology in American Water Development" by Ackerman and Lof, the Johns Hopkins Press, Baltimore, Md. PA1 II. "Pipeline Design for Water Engineers" by Stephenson, Elsevier Scientific Publishing Company, New York, 1981.
Concomitant with the expansion of water transmission networks has been the development of improved piping techniques. For example, the DeLavaud process permitted a practical and improved centrifugal casting of pipe used in water supply networks, while in about 1948 further improvements in pipe construction were evidenced by the development of ductile iron pipe having important strength and corrosion resistance properties. To provide for practical assembly of pipeline matrix components, a variety of joining devices and techniques have been developed. The more popular of these approaches to joining pipe is referred to as a "bell-and-spigot" joint or push joint which is made by slipping a male or spigot end of one pipe section into the bell end of an adjacent pipe essentially until contact is made at the base of the bell. A flexible gasket positioned within the joint assures its water-tight integrity. As may be apparent, this construction is popular both due to the lowering of labor requirements for assembly and due to the simplicity and lower cost of pipes intended for such joining provisions.
A related joining approach utilized principally in the assembly of tees, elbows and plugs provides a mechanical joint wherein a flange is fabricated on one end of a such a component or pipe length and a ring-shaped gland is positioned over the adjacent pipe end. By bolting the flange and gland together such that a flexible seal at the joint is compressed, a water-tight union is achieved. The pull-apart resistance or strength of such joint has been enhanced through the use of set screws in conjunction with the bolted gland, however, resort to such a joining technique in typically encountered lengthy runs of piping is both impractical and unduly expensive.
The design of a municipal piping matrix necessarily involves very long pipelines evidencing numerous directional changes and the resultant use of elbows and attendant joints as well as tee components leading to fire hydrants or user entities. Thus, not only are bursting pressure stresses, pipe weight considerations, superimposed loads as are associated with back fill, water hammer stresses and the like contemplated by the designer, but also the longitudinal forces which become active whenever there is any change in the horizontal or vertical alignment of a length of pipeline must be accommodated for. In this regard, see the following publication:
Without an appropriate accommodation, these longitudinal forces will cause pipe joints to separate. Accordingly, early pipeline design approaches resorted to the use of concrete thrust blocks at each pipeline bend which were structured to counteract: (a) the dynamic thrust due to change in direction of water flow, and (b) the thrust in the direction of each leg of a bend due to water pressure in the pipe.
One successful approach to assuring joint integrity against the above-described thrust forces has been through resort to tying techniques wherein spaced but adjacent flanged joint components are tied together by elongate thrust rods. To simplify the tying procedure, such innovations as "Tiebolts" have evolved to simplify thrust rod placement. See in this regard U.S. Pat. No. 3,144,261. A condition often occurs wherein the thrust rods used in tying a directional changing joint to an elongate run of pipe presents a condition wherein an anchoring flange is not available to provide a rearwardly disposed thrust rod connection. Under these conditions, a conventional retainer clamp has been affixed to a length of such rearwardly disposed bell-and-spigot jointed pipe. The clamps have been of purely conventional design, two clamp components being bolted over the outer circumference of the pipe and retained in place on the pipe by clamping pressure. Thrust rods then were attached to the clamp outwardly of the bolts holding the clamp to the pipe and extended along and parallel to the pipe for attachment to the flanged component. In order to obtain sufficient anchorage, the assembly team must position the retainer clamp a sufficient distance rearwardly along the length of pipe to provide for the resistances achieved by the mass of pipe itself, friction with the trench, associated back fill and the like. As a consequence, thrust rods of lengths approaching 200 feet have not been an unusual encounter.
Over the recent past, traditional retainer clamps have been tested for their capability of anchoring thrust rods against typically encountered joint restraint loads. Depending upon the water pressure, pipe diameters and the like, such loads will vary from about 10,000 pounds total thrust to about 40,000 pounds of thrust. Where conventional clamps have been tested as they are affixed to straight or unaltered lengths of conventional ductile iron pipe, the clamps will commence to slip at about 5,000 to 8,000 pounds of thrust or pull. Considering that a failure for a joint is one wherein movement between the male and female components takes place, any significant clamp slippage under these thrust loads will result in an unacceptable tying procedure. Usually, a slippage in excess of about 0.74 inches is considered to constitute a joint failure, it being understood, that in the assembly of the components, variations in the degree of seating between mated components will occur.
Generally, in order to achieve a satisfactory and fully reliable tying system wherein clamping techniques must be used, a thrust load resisting capability of 44,000 pounds should be achievable in order to provide adequate factors of safety. This thrust load anchoring capability must be achievable under clamping conditions wherein no buttressing otherwise available from the bell-and-spigot configuration itself is at hand, i.e. the clamping technique must be usable on straight sections of pipe. To the time of the instant invention, such capability for providing adequate tired joint restraint overcoming thrust loads has not been available.